Furnace with separable sections for heating silicon steel strip



' Mai-ch 17, 1970 H. B. FOIIQSLUND FURNACE WITH-SEPARABLE SECTIONS FORHEATING SILICON STEEL STRIP Original Filed Jan. 7, 1965 4 Sheets-Sheet 1March 17, 1970 H. B. FORSLUND FURNACE WITH =SEPARABLE SECTIONS FORHEATING SILICON STEEL STRIP 4 Sheets-Shet 2 Original Filed Jan. '7, 1965March 17, 1970 FORSLUND 3,501,135

FURNACE WITH SEPARABLE SECTIONS FORHEATING SILICON STEEL STRIP OriginalFiled Jan. 7, 1965 4 Sheets-Sheet 5 March 17, 1970 H. B. FORSLUND3,501,135

FURNACE WITH SEPARABLE SECTIONS FOR HEATING SILICON STEEL STRIP OriginalFiled Jan. 7, 1965 4 Sheets-Sheet 4 United States Patent 3,501,135FURNACE WITH SEPARABLE SECTIONS FOR HEATING SILICON STEEL STRIP HerbertB. Forslund, Williamstown, Mass., assignor to General Electric Company,a corporation of New York Original application Jan. 7, 1965, Ser. No.424,081, now Patent No. 3,409,480. Divided and this application May 13,1968, Ser. No. 752,085

Int. Cl. C21d 9/56, 9/68; C22c 39/44 U.S. Cl. 266-3 12 Claims ABSTRACTOF THE DISCLOSURE Furnace apparatus for heating silicon steel stripcomprises a first furnace section for heating the steel strip in strandform as it moves through this section, and an adjoining second furnacesection for heating the strand in coiled form at a higher temperature,the furnace sections being separable.

This application is a division of co-pending application Ser. No.424,081, filed Jan. 7, 1965, and assigned to the same assignee as thepresent invention, now Patent 3,409,480, issued Nov. 5, 1968.

The present invention relates to a furnace apparatus and method forprocessing metal strip material, and more particularly to such apparatusand method for heat treatment of magnetic silicon steel for electricaluses such as in transformers, motors and other electromagneticapparatus.

The silicon steel material to which this invention relates is usuallyreferred to in the art as flat rolled electrical steel and isconventionally composed principally of iron alloyed with about 1-4%silicon, preferably 2.5 to 3.5% silicon, and containing relatively minoramounts of various impurities such as sulfur, manganese and phosphorusand having low carbon content as finished material.

In the processing of silicon steel strip of the above type to producematerial of good magnetic and electrical properties, the strip isnormally subjected, after a series of rolling stages, to an annealingtreatment in which two purposes are sought to be accomplished. First,the anneal should develop in the steel a crystal structure (texture) sooriented that good magnetic properties are obtained in the strip. Thegrain orientation of the steels produced by this process may be ofdifferent types such as those referred to as the (110) [001], (100)[001], or other types, the. notations being in Miller indices, asunderstood in the art. Such crystal structures are usually developed bysecondary recrystallization, as explained below. Second, the annealshould remove impurities such as sulfur and carbon which may causeexcessive watt loss in the oriented strip. In general, low watt losscannot be obtained without good crystal orientation and without suitablepurification of the material.

By secondary grain growth, or secondary recrystallization as referred toherein, is meant the process whereby in the final texture-producingannealing treatment, strainfree crystal grains grow in size by absorbingeach other. Such secondary grain growth usually follows primaryrecrystallization, which is a process whereby the distorted grainstructure of a cold worked metal is replaced by a new strain-free grainstructure by annealing above a specific minimum temperature. It is thesecondary recrystallization that produces the highly preferredorientation sought in high quality magnetic strip, and the orientationthus obtained is usually completely different from that obtained merelyas the primary recrystallization.

3,501,135 Patented Mar. 17, 1970 The magnetic strip is generally in aprimary recrystallized state when it is ready for the final hightemperature anneal. The grains in a primary recrystallized material areon the average considerably smaller than those of a secondaryrecrystallized material and, also, while primary recrystallized stripusually has only a small percentage of orientation, e.g., 15-20%, thelarge grained secondary recrystallized strip has a much higher degree oforientation, with values of 70-95% being the rule.

-It has previously been foundthat in order to develop the maximum degreeof secondary recrystallization in the annealing stage, the heattreatment is best carried out at a temperature which is lower than theoptimum purification temperature. For example, a temperature of 925 C.for grain growth and of 1175 C. for purification has been taught by theprior art. In such processes, the steel strip was held at the lowertemperature for a substantial period of time, at least several hours, toallow adequate grain growth (secondary recrystallization), after whichthe strip was subjected for several more hours to the higher purifyinganneal temperature.

In the patent to Fitz et al. 2,986,485, there is disclosed the treatingof silicon steel strip by a continuous strand annealing method whereinthe period allotted for the two annealing stages are markedly reduced,so as to considerably shorten the overall time required to produce highquality electrical steel. It has been found, however, that all lots ofsilicon steel, for reasons not full known, do not respond favorably tosuch rapid annealing procedures. It appears, for example, that certainsilicon steel is characterized by relatively slow crystal growth at theoptimum growth temperatures, for example, over 900 C., and accordinglyit is necessary to hold such steel for a sufficiently long period at theproper annealing temperatures to ensure completion of secondaryrecrystallization to produce high quality steel strip. On the otherhand, unsatisfactory results have been experienced with certain siliconsteel where it has been held too long at the lower annealingtemperatures, specifically, in the range of about 800 C. to about 900 C.Thus, it appears that due to characteristics of certain silicon steels,the properties of the finally processed steel are degraded by heatingtoo slowly at the lower temperature stages (i.e., 800 to 900 0.),whereas inadequate crystal grain growth results in certain silicon steelif heated for too short a period at the higher annealing temperatures(i.e., over 900 C.). The variability which characterizes silicon steelin these respects occurs not only as between different lots of steel butalso within the same lot.

It is an object of the present invention to provide an apparatus andmethod for processing silicon steel which overcomes the abovedisadvantages.

It is another object of the invention to provide a furnace apparatus forannealing of silicon steel strip subject to the above discussedcharacteristics, wherein the annealing. is carried out at least in parton a continuous basis.

.It is another object of the invention to provide a furnace apparatusand method having a combination of strand annealing and batch annealingfeatures for optimum processing of silicon steel of the above type.

t It is a particular object of the invention to provide a furnaceapparatus which provides for relatively short pre-heating of siliconsteel strip and thereafter for relatively longer heating at higher graingrowth and purifica- 1 tion temperatures.

Other objects and advantages will become apparent from the followingdescription and the appended claims. With the above objects in view, thepresent invention concerns in one of its embodiments a furnace apparatusand method for processing electrical silicon steel which provides forrapidly heating the steel strip to a temperature of not less than about900 C.950 C., and for thereafter heating the steel at a temperaturebetween about 950 C. to about 1050 C. for a period sufiicient tosubstantially complete secondary recrystallization thereof and then at atemperature between about 1100 C. and 1200 C. for a period sufficient topurify the steel.

In accordance with a preferred embodiment, the furnace apparatus of theinvention comprises a first elongated furnace chamber for passing astrand of silicon steel therethrough and for rapidly heating the steelstrand to a temperature of not less than about 900950 C., and a secondfurnace chamber for receiving the thus-heated silicon steel and forheating it to a temperature between about 950 C. to about 1200 C. for arelatively longer period than in the first furnace chamber. In apreferred arrangement, the second furnace chamber includes means forreeling the preheated silicon steel strand into a coil, in which form itis heated to a terminal temperature within the last mentionedtemperature range.

The invention will be better understood from the following descriptiontaken in conjunction with the accompanying drawings, in which:

FIGURE 1 is a plan view in horizontal section of an embodiment of thefurnace apparatus of the invention;

FIGURE 2 is an elevational view in vertical section of the FIGURE 1furnace apparatus;

FIGURE 3 is an exploded perspective view of the entrance portion of thefurnace apparatus;

FIGURE 4 is a perspective view of another portion of the furnaceapparatus; and

FIGURE 5 is a sectional view of the furnace unit shown in FIG. 4, withthe unit in raised position.

Referring now to the drawings, and particularly to FIGURES 1 and 2,there is shown a furnace assembly comprising a pre-heating furnace A anda high temperature annealing furnace B which communicates with oneanother, but which are separable from each other at their adjoiningconnecting housings 31, 32 as more fully described hereinafter. Pre-heatfurnace A has, at its opposite end, a housing 1 connected theretoforming an entrance chamber, as shown more clearly in FIGURE 3, housing1 being removably secured to pre-heat furnace section 2 by bolts orother suitable means and opening into the chamber of section 2 throughan aperture 3. Entrance chamber 1 is equipped with a turntable 4 forrotatably supporting a coil of steel 6 to be processed. Chamber 1 isopen at its sides as shown to provide ready access to its interior, andthereby facilitate placement therein of the coiled steel strip. A cover5 with walls complementary to those of housing 1 is provided for closingthe latter during operation of the furnace, and it is normally movedvertically with the aid of hook 5a for movement into and out of closedposition over chamber 1. Suitable gasketing 1a is provided to afford agas-tight seal between cover 5 and housing 1. synchronously driven pinchrollers 7, 8 are arranged in chamber 1 adjacent aperture 3 to reeeiveand move steel strand 9 through aperture 3 with the plane of the stripvertical as it unwinds from coil 6. A door 10 is provided for closingaperture 3 as shown in FIGURE 3, the door being movable upwardly to theposition shown in FIGURE 2 to uncover aperture 3 to allow passagetherethrough of strip 9 during operation of the furnace.

Furnace section 2 comprises an enclosed elongated heating chamberthrough which steel strand 9 is continuously passed while being heatedduring its movement toward and into high temperature anneal furnace B.During this passage, strip 9 rests at its lower edge on horizontalrollers 11 as it is moved and guided by synchronously driven pairs ofopposed vertical rollers 12 arranged along the path of strip 9. Furnacechamber 2 has heating elements 13 and 14 arranged along its oppositeinner sidewalls for raising the temperature of strip 9, as disclosedhereinafter, as it passes through pre-heat chamber 2. At its exit end,furnace section 2 has an aperture 15 through which strip 9 leaves thepre-heat chamber and a door 16 closes aperture 15 when lowered from theraised position shown in FIGURE 2.

Arranged adjoining the exit end of furnace section 2 during operation ofthe furnace assembly is shown a bell furnace 17 formed of a domedenclosure open at its bottom and provided with supporting legs 17aattached at its bottom. Furnace 17 has an entrance aperture 18 throughwhich steel strip 9 may enter and which is closed by a liftable door 19similar to doors 10 and '16 previously described. Vertical pinch rollers20, 21 at entrance aperture 18 receive strip 9 and move it toward theinterior of bell furnace 17, where a spindle 22 is rotatably mounted forwinding strip 9 into coil form. Spindle 22 is an integral part ofplatform 23 which in turn is carried by turntable 24, the latter beingdriven by motor 25 through suitable gearing means. The arrangement issuch, as seen in FIG. 2, that when furnace 17 is in lowered operativeposition supported by legs 17a, platform 23 is free to rotate withinstationary furnace 17. Platform 23 has a hollow interior of annular formfilled with heat insulating material. Platform 23 is also formed with aradially extending peripheral base portion which has a furtherperipheral extension 26 forming an annular trough for holding liquidsealing material, e.g., molten Woods metal, such that annular projection27 which extends downwardly from the bottom of bell furnace 17 isimmersed in the sealing material and thereby seals off the bottom of thebell furnace during rotation of platform 23. In the embodimentillustrated, as best seen in FIGURE 1, spindle 22 is tubular and isformed with a slot 22 through which the leading end of steel strip 9 isreceived at the start of the reeling operation. Extending verticallythrough the hollow interior of reel 22 and aligned axial passages inplatform 23 and turntable 24, as shown more clearly in FIGURE 5, is anactuating arm 28 pivotally attached intermediate its ends by pivot pin28' to platform 23 for turning about a horizontal axis and detachablyconnected at its lower end (when furnace '17 is in operative assembly)to a switch mechanism 29 which effects the starting of motor 25. Thearrangement is such that the leading edge of strip 9 passes into thehollow interior of reel 22 through slot 22' and strikes the upperportion of arm 28 resulting in the latter turning about its pivot 28'and actuating the motor starting switch 29 at its lower end to initiatethe coil reeling operation.

Along the interior wall of bell furnace 17 is arranged heating element30 for raising the temperature of the furnace to a suitable level, ashereinafter described. At the side adjoining preheat section 2, bellfurnace 17 is formed with an entrance chamber housing 31 which mateswith a corresponding exit chamber housing 32 formed in the adjoining endof preheat section 2 to form a composite connecting chamber. The matingportions of housings 31 and 32 include complementary peripheral recesseswhich together form a groove for receiving a resilient sealing gasket33, made of suitable heat resistant material such as a silicone rubbertubing, attached to one or the other of housing 31 or 32, so that gasket33 effectively seals the joint between the pre-heat furnace section 2and bell furnace 17 when these units are brought into assembly with oneanother as shown. Connecting housings 31, 32 are also each preferablyformed with interior passages 31a, 32a, respectively, through whichcooling liquid may be circulated in order to keep gasket 33 sufficientlycool to avoid undue damage thereto.

The construction of bell furnace '17 as described makes it readilymovable into and out of assembly with furnace section 2, so that afterstrip 9 is fully reeled therein into a coil, bell furnace 17 may beremoved to a different location for continuing the annealing process ofthe steel coil, while a replacement bell furnace is moved into assemblywith pre-heat furnace section 2 to receive another pre-heated strip ofsilicon steel therefrom. For this purpose, a carrying cradle 34 isprovided for holding bell furnace 17 including platform 23, the latterresting on cradle 34 in the carrying position. Thus, at the end of thecoil reeling operation, the lifting of cradle 34 by means of its hooks34a, b raises platform 23 off turntable 24, and the radially projectingbase of platform 23 then engages the bottom of the dome portion offurnace 17 as it rises, so that the unit may be removed with the steelcoil therein, as shown in FIGURE 5. The lower ends of pinch rollers 20,21 are provided with shaft portions or other suitable connectionsseparable from drive motor 35 so that rollers 20, 21 may be readilydisengaged from motor 35 during the removal of bell furnace 17.

To facilitate the assembly and disassembly of furnace units 2 and 17relative to one another, furnace section 2 is preferably provided withwheeled supports 36, 37 and entrance chamber 1 is supported on a mobilecarriage 38, whereby furnace section 2 with attached entrance chamber 1may be rolled toward and away from the position occupied by bell furnace17. Thus, to disassemble the connected units, furnace section 2 isrolled away from furnace 17 a short distance to break the seal at thegasketed joint therebetween and provide the necessary clearance topermit bell furnace 17 to be lifted off from its operating position.After a replacement bell furnace is lowered into operating position,section 2 is rolled toward it until the adjoining housings 31 and 32mate with each other and gasket 33 is compressed therebetween to form agas-tight seal between the furnace units.

It will be understood that the component parts of the assembly asillustrated in the drawings are shown somewhat schematically and therelative sizes of the devices as drawn, particularly the length ofpre-heat furnace section 2, are not intended necessarily to correspondto those used in actual practice.

In the operation of the apparatus disclosed, a coil 6 of rolled siliconsteel strip, e.g., about 11 to 14 mils thick and about 30-36 incheswide, which is to be heat treated for optimum grain growth andpurification and on the surfaces of which an insulating separatorcoating such as magnesium hydroxide has been applied, is placed onturntable 4 in entrance chamber 1 with the coil axis vertical,

and the free end of steel strand 9 is then threaded between pinchrollers 7, 8. Cover 5 is then placed in position, and with door tofurnace section 2 closed, chamber 1 is purged with nitrogen by suitablemeans, not

shown. After the nitrogen purge, pure dry hydrogen gas is introducedinto chamber 1 and all doors 10, 16 and 19 .are opened to providecommunication from chamber 1 through pre-heat chamber 2 to the interiorof bell furnace 17, all portions of the itnerior of the furnace assembly-thus being filled with the hydrogen atmosphere. Steel strip 9 is thenrapidly threaded through the guide rollers in section 2 and bell furnace17 until the leading edge of strip 9 strikes actuating arm 28 in bellfurnace 17, as previously described, to start the reeling operation.Sensing switch 29 also initiates a synchronous drive train (not shown)which synchronously drives rollers 7, 8, 12, and 21, as well asturntable drive motor 4a in entrance chamber 1 and turntable drive motorbelow bell furnace 17. The temperature within pre-heat furnace chamber 2is held at a level such that, taking into account the speed of travel ofthe steel strip through furnace 2 and other factors, the temperature ofthe moving steel strand is raised from .room temperature to about 950C.-975 C. by the time it reaches the exit end of furnace 2. Preferably,the temperature of furnace 2 is maintained such that there is a gradientbeginning at about 500 C. at the entrance end to about 1000 C. at itsexit end. In general, it is desirable to employ furnace temperaturesdesigned to bring the steel gradually but rapidly to a temperature aboveabout 900 C. The length of pre-heat chamber 2 and the speed of movementof steel strip 9 therethrough will be governed mainly by productionrequirements. Thus, in general, for

larger production levels, the rate of the steel strip movement will befaster and thus require a longer pre-heat chamber to enable the strip toattain the desired temperature by the time it reaches the exit end. Toavoid degradation of the steel properties which might result fromprolonged exposure of the steel in the temperature range of about 800C.900 C., it is essential that the time for any portion of the steel inthis temperature range be less than ten minutes. Tests have shown thatsilicon steel in strand form can be raised from room temperature toabout 975 C. in about twenty seconds where the heating chamber has aheat gradient from 500 C. at the entrance end to 1000 C. at the exitend. In an illustrative arrangement, therefore, the pre-heat chamber 2with such a heat gradient from end to end may be about 17 feet long, andthe steel strand is passed therethrough at the rate of about .85 feetper second. In another arrangement, the rate of movement of the strandmay be 2.85 feet per second through a pre-heat furnace 57 feet long.

During the re-winding of the pre-heated strip 9 in bell furnace 17 asthe strip leaves furnace section 2, the temperature in bell furnace 17is maintained in the range of about 950 C. to about 1050 C. After there-winding of strip 9 into a coil in bell furnace 17 is complete, doors16 and 19 in connecting housings 31, 32 are closed, and the connectingchamber formed between housings 31, 32 is purged with nitrogen. Whenthepurge is complete, pre-heat furnace section 2 is retracted from hellfurnace 17 in the manner previously described, bell furnace 17 andassociated platform 23 are then lifted and transported by cradle 34 to aremote location to complete the balance of the high temperature annealing cycle, another bell furnace is put into position replacing theprevious bell furnace, and pre-heat furnace 2 is moved into assemblywith the new bell furnace for repeating the pre-heating operation asalready described.

In the meantime, the coiled steel in the removed bell furnace is held attemperatures in the range of about 950 C. to about 1200 C. in a reducingatmosphere such as pure dry hydrogen to proivde for continued growth ofcrystals of preferred orientation and to purify the steel by removal ofsulfur and other undesirable impurities. In the grain growth stage, theheating at from about 950 C. to about 1050 C. should be continued for atleast 1 hour and thereafter as long as necessary to accommodate even theslowest crystal growth rate of the variable steels which are processed.It has been found that even those steels which are characterized byrelatively rapid crystal growth are not significantly harmed by heatingfor longer times than necessary during such grain growth temperature(i.e., about 950 C. to about 1050 C.).

Normally, the coil is held in the high temperature stage for chemicalpurification (i.e., about 1100 to about 1200 C.) until the cold spot inthe coil has been at 1150 C. or higher for at least one hour. Theoverall time in this stage may vary from about one hour to well over 24hours, depending upon the rate of chemical purification taking place. Inmost cases, however, not more than two hours is necessary. Thereafter,the coil is usually cooled at the rate of about C. per hour from about1175 C. to about 5 00 C. in the hydrogen atmosphere. The coil is thentransferred to a cooling chamber with a nitrogen atmosphere where it isheld until it reaches a temperature of about 300 C. Removal of the coilfrom this cooling chamber completes the processing cycle.

A number of advantages are obtained in the use of the described methodand apparatus in processing electrical grade silicon steel. By rapidlypre-heating the steel in strand form in the present of the hydrogenatmosphere, the water present in the magnesium hydroxide slurry coatingis quickly removed so that minimum reaction of the water with the steelis permitted. Reaction of the water with the silicon steel forms silicawhich in turn reacts with the magnesia coating, leaving less magnesiafor the subsequent desulfurizing action, to which the magnesiacontributes, in the purifying anneal. Thus, rapid removal of the waterin the strand pre-heating step preserves the magnesia coating andenables the use of thinner coatings of magnesium hydroxide withoutsacrifice in the intended function of this material. Moreover, the rapidpre-heating cycle brings the steel strand quickly through the criticaltemperature of about 800 C.-900 0., wherein certain steels are subjectto marked degradation of properties if held too long at suchtemperatures, such as often occurs in coil heating procedures. It isbelieved that during a slow heat-up rate, the sulfide particles in thesteel, which aid in oriented steel crystal growth but which are criticalas to size and dispersion, may possibly undergo a change in conditionand thereby fail to contribute to the optimum orientation sought. Incombination with the foregoing advantages of ripid pre-heating, thedescribed apparatus provides the further advantage of heat treatingcoils of the steel at optimum crystal growth temperatures for as long aperiod as necessary for completion of the slowest crystal growth, andthis cycle proceeds without interfering with or delaying the rapidpre-heat processing of the steel.

It will be understood that modifications can be made in the apparatusshown while still obtaining the benefits of the invention. For example,instead of employing removable bell furnaces as shown, it may be founddesirable to use a tunnel-type furnace through which coils of pre-heatedsteel strands pass sequentially through the necessary temperaturegradients required for the grain growth and purifying stages of theanneal. Alternatively, a rotary hearth type furnace may be used for thehigh temperature anneal, wherein the steel strands received frompre-heat chamber 2 may be coiled in place at spaced positions on therotary hearth which rotates intermittently, so that each coil ismaintained for a sufiicient period of time at the various annealingtemperature ranges during its travel around to its discharge station.

While the present invention has been described with reference toparticular embodiments thereof, it will be understood that numerousmodifications may be made by those skilled in the art without actuallydeparting from the scope of the invention. Therefore, the appendedclaims are intended to cover all such equivalent variations as comewithin the true spirit and scope of the invention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. Furnace apparatus for heating silicon steel strip material comprisinga first furnace device having an elongated first chamber, means forcontinuously moving a strand of silicon steel through said elongatedfurnace chamber with the plane of the strand substantially vertical,means for raising the temperature of said steel strand in said chamberto at least about 900 C. in less than ten minutes, and a second furnacedevice associated with said first furnace device for receiving thethus-heated silicon steel and heating the same at a temperature of about950 C.-1200 C. for at least two hours, said second furnace device havingmeans for reeling the silicon steel strand into coiled form and forholding the same in coiled form during its heat treatment therein.

2. Furnace apparatus for heating silicon steel strip material comprisingfirst furnace device having an elongated furnace chamber, means forcontinuously moving a strand of silicon steel through said elongatedfurnace chamber, means for raising the temperature of said steel strandin said chamber to at least about 900 C. in less ten minutes, and aseocnd furnace device removably connected in gas-tight relation to saidfirst furnace device for receiving the thus-heated silicon steel andheating the same at a temperature above 900 C.

3. Furnace apparatus for heating silicon steel strip material comprisinga first furnace device having an elongated furnace chamber, means forcontinuously moving a strand of silicon steel through said elongatedfurnace chamber with the plane of the strand substantially vertical,means for raising the temperature of said steel strand in said chamberto at least 900 C. in less than ten minutes, and a second furnace deviceremovably connected in gas-tight relation to said first furnace devicefor receiving the thus-heated silicon steel and heating the same at atemperature of about 950 C. to about 1200 C. for at least two hours,said second furnace device having means for reeling the silicon steelstrand into coiled form and for holding the same in coiled form duringits heat treatment therein.

4. Furnace apparatus for heating silicon steel strip material comprisinga first furnace device having an elongated furnace chamber with anentrance end and an exit end, entrance housing means at the entrance endof said elongated furnace chamber and having rotatable support means forholding a coil of silicon steel strip material, means for unwinding saidsilicon steel strip material and for continuously moving the same in astrand through said elongated furnace chamber with the plane of thestrand substantially vertical, means for raising the temperature of saidsteel strand in said chamber to at least about 900 C. in less than tenminutes, and a second furnace device associated with said first furnacedevice at the exit end thereof for receiving the thus-heated siliconsteel strip material and heating the same at a temperature of about 950C. to about 1200 C. for at least two hours.

5. Furnace apparatus for heating silicon steel strip material comprisinga first furnace device having an elongated furnace chamber with anentrance end and an exit end, entrance housing means at the entrance endof said elongated furnace chamber having rotatable support means forholding a coil of silicon steel strip material, means for unwinding saidsilicon steel strip material and for continuously moving the same in astrand through saidelongated furnace chamber with the plane of thestrand substantially vertical, means for raising the temperature of saidsteel strand in said chamber to at least about 900 C. in less than tenminutes, and a second furnace device associated with said first furnacedevice at the exit end thereof for receiving the thus-heated siliconsteel strip material and heating the same at a temperature of about 950C. to about 1200 C. for at least two hours, said second furnace devicehaving means for reeling the silicon steel strand into coil form and forholding the same in coil form during heat treatment therein, saidrotatable support means, said means for unwinding and continuouslymoving said strand, and said reeling means being synchronously drivenfor uniformly moving said silicon steel strip material.

6. Furnace apparatus for heating silicon steel strip material comprisinga first furnace device having an elongated furnace chamber with anentrance end and an exit end, entrance housing means at the entrance endof said elongated furnace chamber having rotatable support means forholding a coil of silicon steel strip material, means for unwinding saidsilicon steel strip material and for continuously moving the same in astrand through said elongated furnace chamber with the plane of thestrand substantially vertical, means for raising the temperature of saidsteel strand in said chamber to at least about 900 C. in less than tenminutes, a second furnace device associated with said first furnacedevice at the exit end thereof for receiving the thus-heated siliconsteel strip material and heating the same at a temperature of about 950C. to about 1200 C. for at least two hours, said second furnace devicehaving means for reeling the silicon steel strand into coil form andholding the same in coil form during its heat treatment therein, andmeans in said second furnace device operable by the leading edge of thesilicon steel strand as it enters the second furnace device forinitiating the operation of said reeling means.

7. Furnace apparatus for heating silicon steel strip material comprisinga first furnace device having an elongated furnace chamber, means forcontinuously moving a strand of silicon steel through said elongatedfurnace chamber with the plane of the strand substantially vertical,means for raising the temperature of said steel strand in said chamberto at least about 900 C. in less than ten minutes, a second furnacedevice associated with said first furnace device for receiving thethus-heated silicon steel and heating the same at the temperature ofabout 950 C. to about 12 C. for at least two hours, said second furnacedevice having means for reeling the silicon steel strang into coiledform and for holding the same in coiled form during its heat treatmenttherein, and stationary drive means for operating said reeling means insaid second furnace device, said second furnace device with said coilholding and reeling means being removably connected to said stationarydrive means.

8. Furnace apparatus for heating silicon steel strip material comprisinga first furnace device having an elongated furnace chamber, means forcontinuously moving a strand of silicon steel through said elongatedfurnace chamber, means for raising the temperature of said steel strandin said chamber to at least about 900 C. in less than ten minutes, asecond furnace device arranged adjacent said first furnace device forreceiving the thus-heated silicon steel and for heating the same at atemperature above about 900 C., said first and second furnace devicesbeing formed with complementary connecting housing portions defining inthe assembly of said furnace devices an intermediate chambertherebetween, and means for closing off said intermediate chamber fromthe interiors of both said furnace devices.

9. Furnace apparatus for heating silicon steel strip material comprisinga first furnace device having an elongated furnace chamber, means forcontinuously moving a strand of silicon steel through said elongatedfurnace chamber, means for raising temperature of said steel strand insaid chamber to at least about 900 C. in less than ten minutes, and asecond furnace device adjacent to said first furnace device forreceiving the thus-heated silicon steel and heating the same at atemperature above 900 C., said first furnace device being movable toinoperative position away from said second furnace device, and tooperative position toward said second furnace device, said secondfurnace device being movable away from its operative position adjacentsaid first furnace device.

10. Furnace apparatus for heating silicon steel comprising, incombination, first furnace means for pre-heating the silicon steel insingle strand form, and second furnace means movably associated withsaid first furnace means for heating the pre-heated silicon steel in theform of superposed layers.

11. Furnace apparatus for heating silicon steel comprising, incombination, first furnace means for pre-heating the silicon steel insingle-strand form, and second furnace means removably associated withsaid first furnace means for heating the pre-heated silicon steel incoiled form.

12. Furnace apparatus for heating silicon steel comprising, incombination, first furnace means for pre-heating the silicon steel insingle strand form, second furnace means removably associated with saidfirst furnace means for heating the pre-heated silicon steel in coiledform, and means for moving the silicon steel strand through said firstfurnace means and into said second furnace means and for reeling thesame into a coil in said second furnace means.

References Cited UNITED STATES PATENTS 1,646,498 10/1927 Seedc 266-32,169,314 8/1939 Wilson 266--3 2,441,500 5/1948 Miess 266-3 X FOREIGNPATENTS 145,843 6/1954 Sweden. 170,138 1/1960 Sweden.

WILLIAM J. STEPHENSON, Primary Examiner R. S. ANNEAR, Assistant ExaminerAme .l .44

Patent No.

Inventor) I: g}: t I z i z. 1

UNXTED S'IIATES PATENT OFFICE CERTIFICATE OF CORRECTION Dated mum 11.121g It is certified that error appears in the above-identified patentand that said Letters Patent are Col. 2,

line line 28,

line 36,

line- 50,

line

line

line

line 64,

hereby corrected as shown below:

"full" should be fully "oom'rmmicates" should be communicate "interioris misspelled "provide" is misspelled before "ten'Y the viord thanshould belhserteq.

the were "-seeo n g il" 1: iuss pelled delete the were "and" the wordstrand"- is misspelled Signed and sealed this 4th day of'Apgust 1970(SEAL) Attes-tl EDWARD M.FLETCHER,JR.

Attestipg Officer Commissioner of Pstents WILLIAM E. SCHUYLBR, JR.

